The present disclosure relates to a rear radiation type solid-state imaging device, a method of manufacturing the solid-state imaging device, and an electronic apparatus using the solid-state imaging device.
In the related art, a CCD type solid-state imaging device and a CMOS type solid-state imaging device have been proposed as solid-state imaging devices that are used in digital cameras or video cameras. In such solid-state imaging devices, a light receiving section is formed in each of a plurality of pixels formed in a two-dimensional matrix and a signal charge is generated in the light receiving section in accordance with the amount of light received. Further, the signal charge generated in the light receiving section is transferred and amplified, thereby acquiring an image signal.
Common solid-state imaging devices of the related art are surface type solid-state imaging devices that are equipped with a substrate with electrodes or wires on the surface and radiate light from above. For example, in surface type and CMOS type solid-state imaging devices, photodiodes (PD) of the light receiving sections of the pixels are formed inside the silicon substrate and a plurality of wire layers are formed on the silicon substrate through an interlayer insulating film. Further, a color filter and an on-chip lens are disposed above the wire layers. In the surface type solid-state imaging device, light travels into the photodiodes of the light receiving section through the color filter and the wire layers from the on-chip lens.
However, there is a problem in that as the solid-state imaging device is miniaturized, the pitches of the wires decrease while the wire layers become multi-layered, such that the distances between the light receiving sections on the on-chip lens and the silicon substrate increase. With the multi-layering of the wire layers, a portion of incident light traveling at an angle is blocked by the wire layers and does not easily reach the light receiving sections on the silicon substrate, such that a phenomenon, such as shading, occurs.
Recently, a rear radiation type solid-state imaging device that radiates light from a side opposite to the side where the wire layers are formed on the substrate has been proposed (see Japanese Unexamined Patent Application Publication No. 6-283702). In the rear radiation type solid-state imaging device, since a wire layer or a circuit device is not disposed at the side from which light is radiated, it is possible to achieve an effective aperture ratio of 100% of a light receiving section formed on a substrate whereby incident light travels into the light receiving section without reflecting from a wire layer. Therefore, there are great expectations of considerably improving sensitivity and eliminating shading in the rear radiation type solid-state imaging device.
In the rear radiation type solid-state imaging device, it may be preferable to improve the maximum cumulative dosage (Quantity of saturated charges; Qs) of photoelectric-converted charge in the photodiode or widen the area of the photodiode in the depth direction of the substrate, in order to improve the dynamic range, which is the basic performance. However, when the photodiode is expanded close to the light receiving surface, the distance from the output terminal increases, such that it is difficult to completely transfer the charges accumulated in the photodiode, which causes a residual image. As an improvement plan, a solid-state imaging device equipped with a vertical transistor having a reading electrode (trench type electrode) corresponding to a photodiode has been proposed (see Japanese Unexamined Patent Application Publication No. 2004-281499 and PCT Japanese Translation Patent Publication No. 2007-531254).
FIG. 19 shows a schematic cross-sectional configuration of a solid-state imaging device equipped with a vertical transistor of the related art. As shown in FIG. 19, two layers of photodiodes PD1 and PD2 are formed in the depth direction of a substrate 101. Vertical gate electrodes 103 and 104 are formed deep in contact with the photodiodes PD1 and PD2, respectively. The vertical gate electrodes 103 and 104 are formed by embedding an electrode material in trench portions formed in desired depths in the substrate 101 through a gate insulating film 102. Floating diffusion portions FD1 and FD2 are formed at the areas adjacent to the vertical gate electrodes 103 and 104, respectively.
In the solid-state imaging device 100 of FIG. 19, signal charges accumulated in the photodiodes PD1 and PD2 are transferred to the floating diffusion portions FD1 and FD2, respectively, by applying a desired voltage to the vertical gate electrodes 103 and 104. In this configuration, it is possible to implement a configuration that can transfer signal charges accumulated in the photodiodes PD1 and PD2 formed in different depths by changing the depths of the trench portions formed on the substrate 10. However, the configuration that changes the depths of the trench portions in the same substrate is difficult implement by a one-time lithography process and etching process, such that it is necessary to repeat the process of forming the vertical gate electrodes 103 and 104 several times. Therefore, considering non-uniformity of the depths of the trench portions or non-uniformity of the process, such as non-uniformity in diffusion of ion injection when forming the photodiodes, it is not practical to design a pixel that can transfer a photoelectric-converted signal charge.
It may be considered to remove the process non-uniformity by applying a vertical transistor composed of vertical gate electrodes formed through a substrate (see Japanese Unexamined Patent Application Publication No. 2008-258316).
FIG. 20 shows a schematic cross-sectional configuration of a solid-state imaging device 105 including a vertical gate electrode formed through a substrate. As shown in FIG. 20, a solid-state imaging device 105 includes a vertical gate electrode 108 that is vertically formed through the horizontal surface of a substrate 106. The vertical gate electrode 108 is formed by forming a through-hole through the substrate 106 and embedding an electrode material through a gate insulating film 107. In the solid-state imaging device 107 of FIG. 20, a signal charge of a photodiode PD formed deep in the depth direction of the substrate 106 can be read out with a floating diffusion portion FD formed opposite to a light receiving side of the substrate 106.
However, when the vertical gate electrode 108 is formed through the substrate 106 shown in FIG. 20, the deep portion of the substrate 106 is damaged by backflow of an etchant when forming the through-hole from the surface side to the rear surface side of the substrate 106. Accordingly, there is a problem on the rear surface side of the substrate 106 in that a carrier is generated at the corners (surrounded by dotted lines ‘a’) continuing from the inner circumferential surface of the end of the through-hole to the rear surface side of the substrate, and a noise is generated by the mixing of the carrier with a carrier (signal) created by photoelectric conversion, such that so-called white points increase.